1. Field of the Invention
The present invention relates to a zoom lens system, and, more particularly, to a zoom lens system composed of two lens groups. The lens has a high magnification zoom ratio of more than 2 times and uses inexpensive lens materials. Good aberration performance is maintained.
2. Description of the Prior Art
In a zoom lens systems, the overall focal length is adjustable with the widest angle of view at the shortest focal length and the narrowest angle of view at the longest focal length.
Recently, compact "lens shutter" cameras have been introduced with automatic features and a zoom lens with a focal length which varies linearly. The lens shutter cameras are required to be compact, light, and inexpensive especially because they are for nonprofessional users.
Generally, zoom lenses for the lens shutter cameras have either two lens groups or three lens groups. The two lens group configuration is preferred for a zoom ratio of about 2 times because a lens barrel for the two lens group can be designed and controlled easily and produced economically.
For example, Japanese Patent Unexamined Publication No. Hei 1-193808 (title: ZOOM LENS FOR COMPACT CAMERAS, published on Aug. 3, 1989) and Japanese Patent Unexamined Publication No. KOKA1 Hei 1-288823 (title: SMALL-SIZED ZOOM LENS, published on Nov. 21, 1989) disclose zoom lenses having two lens groups.
The zoom lens disclosed in Japanese Patent Unexamined Publication No. Hei 1-193808 has a zoom ratio below 1.9 times and uses expensive lens materials. The zoom lens disclosed in Japanese Patent Unexamined Publication No. Hei 1-288823 has many elements, uses aspheric surface lenses made of glass which are expensive, and has a zoom ratio too low to maintain good optical performance.